Single layer small grain size FePT:C film for heat assisted magnetic recording media
FePt-based heat assisted magnetic recording (HAMR) media comprising a thick granular FePt:C magnetic recording layer capable of maintaining a single layer film having desirable magnetic properties. According to one embodiment, the thick granular FePt:C magnetic recording layer comprises a plurality of carbon doped FePt alloy columnar grains, where the plurality of carbon doped FePt alloy columnar grains comprise a carbon gradient along the thickness of the hard magnetic recording layer.
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This invention relates to the field of disk drives and more specifically, to heat assisted magnetic recording media for disk drives.
BACKGROUNDFor all types of substrates, magnetic recording media has begun to incorporate perpendicular magnetic recording (PMR) technology in an effort to increase areal density and is now working toward densities of 800 Gbits/in2. Generally, PMR media may be partitioned into two primary functional regions: a soft magnetic underlayer (SUL) and a magnetic recording layer(s) (RL).
Typically, higher areal densities are typically achieved with well-isolated smaller grains in the PMR layer. A higher magnetocrystalline anisotropy constant (Ku) is typically required to resist the demagnetization effects of the perpendicular geometry and to keep the smaller grains thermally stable to reduce media noise.
With the advent of heat-assisted magnetic recording (HAMR) media, areal densities of 900 Gbits/in2 and higher using PMR technology has been realized. This is because HAMR media comprises of a magnetic compound, such as an FePT alloy, that has a higher magnetic stability than PMR technology using non-HAMR media (e.g., CoPt). However, because the HAMR media comprises of such higher-stability magnetic compounds, HAMR media requires that heat be applied to it before changes its magnetic orientation can be changed. Typically, when PMR technology magnetically records data to HAMR media, it first uses a heating element, such as a laser, to increase the temperature of the recording location on the media, in order to lower the location's high magnetic anisotropy constant (Ku) sufficiently to allow a change to its magnetic orientation (i.e., record data).
Unfortunately, in order to provide strong magnetic signal for the reader sensor detection and high signal-to-noise ratio (SNR) in the recording process, HAMR media require a relatively thick hard magnetic recording layer, preferably a thickness above 5 nm. This is particularly problematic for HAMR media that utilize carbon doped iron platinum alloy (FePtX:C) for its hard magnetic layer, as typically a FePtX:C hard magnetic layer having a thicknesses beyond 5-6 nm results in the formation of two or more layers of FePtX:C. This is clearly shown in
The present invention is illustrated by way of example, and not limitation, in the figures of the accompanying drawings in which:
In the following description, numerous specific details are set forth, such as examples of specific layer compositions and properties, to provide a thorough understanding of various embodiment of the present invention. It will be apparent however, to one skilled in the art that these specific details need not be employed to practice various embodiments of the present invention. In other instances, well known components or methods have not been described in detail to avoid unnecessarily obscuring various embodiments of the present invention.
The terms “over,” “under,” “between,” and “on” as used herein refer to a relative position of one media layer with respect to other layers. As such, for example, one layer disposed over or under another layer may be directly in contact with the other layer or may have one or more intervening layers. Moreover, one layer disposed between two layers may be directly in contact with the two layers or may have one or more intervening layers. In contrast, a first layer “on” a second layer is in contact with that second layer. Additionally, the relative position of one layer with respect to other layers is provided assuming operations are performed relative to a substrate without consideration of the absolute orientation of the substrate.
Embodiments of the present invention include a recording medium comprising a hard magnetic recording layer disposed above a soft magnetic underlayer, where the hard magnetic recording layer comprises a plurality of carbon doped FePt or FePt alloy (FePtX) columnar grains, and the plurality of carbon doped FePt alloy columnar grains comprise a carbon gradient along the thickness of the hard magnetic recording layer. For some such embodiments, which include either FePt doped with a carbon gradient or FePt alloys (FePtX) doped with a carbon gradient, the hard magnetic recording layer can achieve thicknesses above 5 nm while maintaining a single layer.
As illustrated by their shading, the FePtX:C columns 507 of the recording layer 505 comprise a carbon (C) gradient along the thickness 506 of the entire hard magnetic layer 505. In some embodiments, the such a graded columns are created by two or more multiple layers (N>2) of FePtX:C films with varying carbon (C) content in each layer. For example, a gradient may be created using a first layer of FePtX:C film having a carbon (C) content of 40% (i.e., FePtX:C40) disposed over the interlayer and heatsink layer 515, and a second layer of FePtX:C film having a carbon (C) content of 20% (i.e., FePtX:C20) disposed over the first layer of FePtX:C film. It would be well understood by one skilled in the art that layers of FePt:C films having different carbon (C) may also be used to create the hard magnetic recording layer with a carbon gradient, and that FePt and FePtX film layers having carbon content different from those discussed here may also be used.
Also depicted is a substrate 525, that may be, for example, a glass, a metal, and/or a metal alloy material. In a particular embodiment, the substrate 525 is disk-shaped or annular. Glass substrates that may be used include, for example, a silica-containing glass such as borosilicate glass and aluminosilicate glass. Metal and metal alloy substrates that may be used include, for example, aluminum (Al), tantalum (Ta), and aluminum magnesium (AlMg) substrates. in an alternative embodiment, other substrate materials such as polymers and ceramics may be used.
The soft magnetic underlayer (SUL) 510 is disposed over the substrate 525. Generally, the SUL 510 may include any materials known in the art. The SUL 510 itself may be a laminate or multilayer stack of a plurality of soft magnetic layers separated by nonmagnetic or antiferromagnetic films. In one exemplary embodiment, the SUL 510 includes a synthetic antiferromagnet (SAF) structure comprising two amorphous soft ferromagnetic layers (e.g., CoTaZr or CoFeTaZr, etc.) antiferromagnetically coupled with one another across a spacer layer (e.g. ruthenium (Ru)) there-between. The thickness of the SUL 510 will generally be in the range of 5 nm to 60 nm.
Disposed over the soft magnetic underlayer (SUL) 510 is an interlayer and a heatsink layer 515. The heatsink layer 515 specifically facilitates heat transfer for the HAMR media. The heatsinky layer may also be useful in alternative embodiments in accordance with the present invention, including thermally assisted magnetic recording (TAMR) or optically assisted magnetic recording (OAMR)). Although the illustrated example embodiment depicts the heatsink layer 515 is disposed between the SUL 510 and the hard magnetic recording layer 505, it should be appreciated the heatsink layer 515 may alternatively be disposed between the SUL 510 and the substrate 525. Generally, regardless of the position within the media structure 500, the heatsink layer 515 is usually a metal (e.g. Cu) or other heat conductive material. In the exemplary embodiment, the heatsink layer 525 may have a thickness between 30 nm and 100 nm.
Although the illustrated embodiment depicts the heatsink layer 515 is disposed between the SUL 510 and the hard magnetic recording layer 505, it should be appreciated the heatsink layer 515 may alternatively be disposed between the SUL 510 and the substrate 525. Generally, regardless of the position within the media structure, the heatsink layer 515 is a metal or other heat conductive material. In the exemplary embodiment, the heatsink layer 515 may be made of copper (Cu) and have a thickness between 30 nm and 100 nm.
Disposed over the hard magnetic recording layer 505 are a soft magnetic layer 521, an overcoat 530, and a lubricant 535. The soft magnetic layer 521 is disposed over the hard magnetic recording layer 505, and may comprise a CoFe or CoCr based soft magnetic alloy. This soft magnetic may contain: Al, B, C, Cr, Cu, N, Nb, Ni, Re, Ru, Si, Ta and/or Zr.
Overcoat 530 is formed on top of the soft magnetic recording layer 521 to meet tribological requirements such as contact-start-stop (CSS) performance and corrosion protection. Materials usually utilized for the overcoat layer 530 include carbon-based materials, such as hydrogenated or nitrogenated carbon. A lubricant 535 is placed on top of the overcoat layer 530 to further improve tribological performance. Exemplary lubricants include a perfluoropolyether or phosphazene lubricant or a composite thereof.
On the other hand, HAMR media 615 comprises of several different layers described above, including a hard magnetic recording layer of 10 nm, comprising a singe layer of FePt:C40. TEM image 609 depicts a two layers of FePt:C forming, due to the thickness of the hard magnetic recording layer being larger than 5 nm.
At operation 820 the interlayer and heatsink layer 515 deposited over the SUL 510 to facilitate heat-assisted perpendicular magnetic recording.
At operation 830, the hard recording layer, comprising two or more layers (N>2) of FePtX:C film, where each film layer has a graded carbon (C) content, is deposited over the interlayer and heatsink layer 515. As discussed above, materials X that can be used in utilized in the FePtX alloy, such as, Ag, Au, B, Cu, Ir, Nb, Ni, Ti, W, or Zr, for example, to stabilize the phase or tune the magnetic properties of the hard magnetic recording layer 505. In some embodiments, the two or more layers of FePtX:C may be deposited using two or more chambers containing FePtX:C material of differing carbon content. For example, to deposit one layer of FePtX:C40 and one layer of FePtX:C20 for the hard magnetic recording layer, one chamber would contain FePtX:C40 material, while another would contain FePtX:C20 material. In some such embodiments, the FePtX:C material is deposited at a pressure between 2 mTorr and 100 mTorr.
At operation 840, a soft magnetic layer 521 is deposited over the hard magnetic recording layer 505. In some embodiments, the soft magnetic layer 521 and the hard magnetic layer 505 may form a graded Hk structure, an exchange coupled composite (FCC) structure or a synthetic antiferromagnetically coupled (SAF) structure. The soft magnetic alloy of the soft magnetic layer 521 may be a FePtX or CoPtX alloy, where X may be Ag, Au, B, Cu, Ir, Nb, Ni, Ti, W, or Zr. In addition, the soft magnetic alloy may also be a disordered structure, having a low anisotropy field and a curie temperature.
Next, in operation 850, an overcoat 530 layer and a lubricant layer 535 are formed over the hard magnetic recording layer 505. Overcoat 530 may be formed on top of the soft magnetic recording layer 521 to meet tribological requirements such as contact-start-stop (CSS) performance and corrosion protection. As discussed above, predominant materials for the overcoat layer 530 are carbon-based materials, such as hydrogenated or nitrogenated carbon. A lubricant 535 may be placed on top of the overcoat layer 530, by dip coating, spin coating, etc., to further improve tribological performance. Example lubricants include a perfluoropolyether or phosphazene lubricant or a composite thereof.
For deposition of each FePtX:C layer of the recording layer 505, a variety of methods known in the art, for example, electroless plating, sputtering (e.g., static or in-line), chemical vapor deposition (CVD), ion-beam deposition (IBD), etc. may be utilized. For example a static sputter systems may be utilized, such as those available from manufacturers such as Intevac Inc. of Santa Clara, California and Carton-Anelva Corp. of Japan. With in-line sputtering systems, disk substrates are loaded on a pallet that passes through a series of deposition chambers the deposit films successively on substrates. In-line sputtering systems are available from manufacturers such as Ulvac Corp. of Japan.
In the foregoing specification, embodiments of the invention have been described with reference to specific exemplary features thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and figures are, accordingly, to be regarded in an illustrative rather than a restrictive sense.
Claims
1. A recording medium comprising:
- a hard magnetic recording layer comprising a plurality of carbon doped FePt alloy columnar grains;
- a soft magnetic layer disposed over the hard magnetic recording layer, the soft magnetic layer comprising a CoFe or CoCr based soft magnetic alloy; and
- a soft magnetic underlayer disposed under the hard magnetic recording layer, wherein the hard magnetic recording layer has a thickness that extends perpendicular with respect to the soft magnetic underlayer;
- wherein the plurality of carbon doped FePt alloy columnar grains comprises a carbon gradient along the thickness of the hard magnetic recording layer.
2. The recording medium of claim 1, wherein the each of the plurality of carbon doped FePt alloy columnar grains comprises a plurality of overlying sub-layers of the carbon doped FePt alloy, wherein differing carbon content of each overlying sub-layer results in the carbon gradient.
3. The recording medium of claim 2, wherein the plurality of overlying sub-layers comprises a first overlying sub-layer having 40 at. % carbon.
4. The recording medium of claim 3, wherein the plurality of overlying sub-layers further comprises a second overlying sub-layer having 20 at. % carbon.
5. The recording medium of claim 3, wherein the first overlying sub-layer when compared to other ones of the plurality of overlaying sub-layers is positioned closest to the soft magnetic underlayer.
6. The recording medium of claim 1, wherein the carbon gradient is such that carbon content within the hard magnetic recording layer is greater closer to the soft magnetic underlayer.
7. The recording medium of claim 1, wherein the carbon gradient is such that carbon content within the hard magnetic recording layer is greater away from the soft magnetic underlayer.
8. The recording medium of claim 1, wherein the thickness of the hard magnetic recording layer is more than 5 nm.
9. The recording medium of claim 1, wherein the FePt alloy in the carbon doped FePt alloy columnar grains is a FePtX alloy, where X comprises Ag, Au, B, Cu, Ir, Nb, Ni, Ti, W, or Zr.
10. The recording medium of claim 1, wherein the thickness of the plurality of carbon doped FePt alloy columnar grains is more than 5 nm.
11. The recording medium of claim 1, further comprising a heatsink layer under the hard magnetic recording layer and above the soft magnetic underlayer.
12. A recording device comprising:
- a housing containing a recording head and a recording medium;
- the recording head for reading magnetic signals from, and writing magnetic signals to, the recording medium; and
- the recording medium comprising:
- a hard magnetic recording layer comprising a plurality of carbon doped FePt alloy columnar grains;
- a soft magnetic layer disposed over the hard magnetic recording layer, the soft magnetic layer comprising a CoFe or CoCr based soft magnetic alloy; and
- a soft magnetic underlayer disposed under the hard magnetic recording layer, wherein the hard magnetic recording layer has a thickness that extends perpendicular with respect to the soft magnetic underlayer;
- wherein the plurality of carbon doped FePt alloy columnar grains comprise a carbon gradient along the thickness of the hard magnetic recording layer.
13. The recording device of claim 12, wherein the each of the plurality of carbon doped FePt alloy columnar grains comprises a plurality of overlying sub-layers of the carbon doped FePt alloy, wherein differing carbon content of each overlying sub-layer results in the carbon gradient.
14. The recording device of claim 13, wherein the plurality of overlying sub-layers comprises a first overlying sub-layer having 40 at. % carbon.
15. The recording device of claim 14, wherein the plurality of overlying sub-layers further comprises a second overlying sub-layer having 20 at. % carbon.
16. The recording device of claim 14, wherein the first overlying sub-layer when compared to other ones of the plurality of overlaying sub-layers is positioned closest to the soft magnetic underlayer.
17. The recording device of claim 12, wherein the carbon gradient is such that carbon content within the hard magnetic recording layer is greater closer to the soft magnetic underlayer.
18. The recording device of claim 12, wherein the carbon gradient is such that carbon content within the hard magnetic recording layer is greater away from the soft magnetic underlayer.
19. The recording device of claim 12, wherein the thickness of the hard magnetic recording layer is more than 5 nm.
20. The recording device of claim 12, wherein the FePt alloy in the carbon doped FePt alloy columnar grains is a FePtX alloy, where X comprises Ag, Au, B, Cu, Ir, Nb, Ni, Ti, W, or Zr.
21. The recording device of claim 12, wherein the thickness of the plurality of carbon doped FePt alloy columnar grains is more than 5 nm.
22. The recording device of claim 12, further comprising a heatsink layer under the hard magnetic recording layer and above the soft magnetic underlayer.
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Type: Grant
Filed: Aug 20, 2010
Date of Patent: Nov 18, 2014
Assignee: WD Media, LLC (San Jose, CA)
Inventors: Hua Yuan (Milpitas, CA), Alexander Chernyshov (San Jose, CA), B. Ramamurthy Acharya (Fremont, CA)
Primary Examiner: Kevin Bernatz
Application Number: 12/860,616
International Classification: G11B 5/667 (20060101); G11B 5/65 (20060101);